This is common GDR3 bug.
Easy way: reflash your phone.
Hard way: do HR by key combination. This may not work, after HR you will still see black screen.
Hard way 2: block screen and unblock it. Reboot phone, it'll boot into desktop, but many things are missing. Do HR in the settings. This may not work, after HR you will still see black screen.
Good news: SamWP8 can change region (for updates, not CSC code) without HR. Choose 000-AT in the list and tap "set". You don't even need to reboot phone, just check for updates.
2 Questions:
Can i flash with latest WINOS and where do i find this tools?
And where do i choose "000-AT in the list" wath region is that, am in Sweden?
I solved the black screen problem with this trick:
Turn off the phone, Once the phone is off, Hold the Volume down key then
plug the charger (charger should be connected to the power source ",)
Once you see the exclamation ( ! ), remove your finger from the button.
Then press the following keys in, Volume Up, Volume Down, Power Key and
Volume down. The phone will turn on automatically, this may take
several minutes and it will show two gears that are spinning just wait
for it to finish.
Can i now update to latest OS vers 8.0.10521.155?